It is well known that for the color development of a silver halide photographic light-sensitive material, after exposure, an oxidized aromatic primary amine developing agent can be reacted with a dye forming coupler to obtain a color image.
It is also known that, for the color development of a silver halide color photographic material, an oxidized aromatic primary amine color developing agent can be reacted with a coupler to form a dye such as an indophenol, an indoaniline, an indamine, an azomethine, a phenoxazine, a phenazine, and the like, thus forming a color image. In this procedure, the subtractive color process is ordinarily used for color reproduction, and silver halide emulsions which are selectively sensitive to blue, green, and red light, and yellow, magenta, and cyan color image formers, which are respectively the complementary colors of blue, green, and red, are employed. For example, a coupler of the acylacetanilide or benzoylmethane type is used for forming a yellow color image; a coupler of the pyrazolone, pyrazolobenzimidazole, cyanoacetophenone or indazolone type is generally used for forming a magenta color image; and a phenolic coupler, such as a phenol and a naphthol, is generally used for forming a cyan color image.
It is also known that, in addition to color couplers which do not have a substituent at the coupling position thereof, and thus require development of 4 mols of exposed silver halide for forming 1 mol of a dye, there are color couplers which have a substituent capable of being released upon color development at the coupling position thereof, and thus require development of only 2 mols of exposed silver halide for forming 1 mol of a dye. The former are known as 4-equivalent couplers, and the latter are known as 2-equivalent couplers.
Color couplers must satisfy various requirements. For example, it is necessary that they have a good spectral property and provide a dye image having excellent stability to light, temperature, and humidity for a long period of time upon color development.
It is also required in a multilayer color photographic light-sensitive material that each coupler is fixed in a layer separated from each other in order to reduce color mixing and to improve color reproduction. Many methods for rendering a coupler diffusion-resistant are known. One method is to introduce a long chain aliphatic group into a coupler molecule in order to prevent diffusion. Couplers according to such a method require a step of addition to an aqueous gelatin solution by solubilizing in alkali, or a step of dispersing in an aqueous gelatin solution by dissolving in a high boiling organic solvent, since the couplers are immiscible with an aqueous gelatin solution.
Another method for rendering a coupler diffusion-resistant is to utilize a polymer coupler obtained by polymerization of a monomeric coupler. However, such polymer couplers have disadvantages, in that they have poor solubility to water, and they increase the viscosity of an aqueous gelatin solution. In order to overcome these disadvantages, polymer coupler latexes have been provided. The method of adding a polymer coupler in a latex form to a hydrophilic colloid composition has many advantages in comparison with other methods. For example, when the polymer coupler latex is used, the step of adding the coupler to a coating solution can be simplified, since the use of a high boiling organic solvent or an alkali is not necessary and a special dispersing method is not required. Further, the deterioration of strength of the film formed is small, because the hydrophobic substance is in a latex form. Also, the thickness of the layer can be reduced, since an organic solvent is not contained therein. Furthermore, since the latex can contain coupler monomers in a high concentration, it is easy to incorporate couplers in a high concentration into a photographic emulsion, and the increase of viscosity is small. Moreover, the crystallization of couplers in the emulsion layer is also prevented thereby.
As a polymer coupler latex described above, for example, a 4-equivalent magenta polymer coupler latex and method of preparation thereof are disclosed in U.S. Pat. No. 4,080,211 and British Pat. No. 1,247,688, a copolymer latex of a competing coupler in West German Pat. No. 2,725,591 and U.S. Pat. No. 3,926,436, and cyan polymer coupler latex in U.S. Pat. No. 3,767,412.
However, these polymer coupler latexes have a number of problems in addition to the many advantages described above, and thus it has been desired to overcome these problems. The problems include the following:
1. The rate of the coupling reaction is poor, and thus the density of dye formed is very low.
2. The light fastness of the magenta color image is very poor.
3. Undesirable fog is readily formed upon color development.
4. The fastness to humidity and heat of the color image is poor.
5. The latexes cannot be stored for a long time since aggregation thereof occurs in solution.
6. The resistance to formalin is very poor.
More particularly, they have major disadvantages in coupling reactivity, resistance to formalin, and light fastness. With respect to the coupling reactivity, no improvement is obtained by using the 2-equivalent magenta polymer coupler latex described in West German Pat. No. 2,725,591 and U.S. Pat. No. 3,926,436. This suggests that there are great differences in photographic properties between conventional couplers and polymer couplers.